Nowadays, cloud computing is used for constructing information networks of enterprises, and virtualization technology may be employed and deployed in cloud computing. A Software Defined Network (SDN) is a solution for virtualization. The SDN may separate the control plane from a forwarding plane in the network, which for example may allow a centralized controller to implement various policies for various forwarding behaviors in the network. Thus, a forwarding device may forward a flow according to a flow entry distributed from the controller.